Touch-sensitive devices allow a user to conveniently interface with electronic systems and displays by reducing or eliminating the need for mechanical buttons, keypads, keyboards, and pointing devices. For example, a user can carry out a complicated sequence of instructions by simply touching an on-display touch screen at a location identified by an icon displayed on the display.
Capacitive touch-sensing devices have been found to work well in a number of applications. In many touch-sensitive devices, the touch input is sensed when a conductive object in the sensor is capacitively coupled to a conductive touch implement such as a pen (also referred to as a stylus) or a user's finger. Generally, whenever two electrically conductive members come into proximity with one another without actually touching, a capacitance is formed therebetween. In the case of a capacitive touch-sensitive device, as an electrically conductive object approaches and/or touches the touch sensing surface, changes in capacitance occurs at the touch location and the sensing circuit can be configured to determine the touch location based on the change in capacitive coupling. In some embodiments, the sensing circuit can recognize that multiple objects are concurrently touching the touch surface and can determine the locations of the objects as they move across the touch surface. Other technologies for touch sensing have also been considered, including resistive, magnetic, optical, and acoustic technologies, for example.